Centrifugal fan

ABSTRACT

A centrifugal fan for use with an engine includes a hub defining a rotational axis, a plurality of blades arranged about the rotational axis, and a screen coupled to the hub and blades for co-rotation therewith. The hub, the blades, and the screen are integrally formed as a single piece.

FIELD OF THE INVENTION

The present invention relates to centrifugal fans, and more particularly to centrifugal fans for use with internal combustion engines.

BACKGROUND OF THE INVENTION

Centrifugal fans draw air from an axial direction and discharge a radial airflow. Centrifugal fans are often used for air-cooling internal combustion engines. Centrifugal fans are typically assembled using a number of components having differing materials. Such components are separately formed and fastened together, thereby increasing manufacturing costs and complexity.

SUMMARY OF THE INVENTION

The present invention provides in one aspect, a centrifugal fan for use with an engine including a hub defining a rotational axis, a plurality of blades arranged about the rotational axis, and a screen coupled to the hub and blades for co-rotation therewith. The hub, the blades, and the screen are integrally formed as a single piece.

The present invention provides, in another aspect, an engine including a crankcase, a cover at least partially enclosing the crankcase, and a centrifugal fan rotatable while the engine is in use for discharging a cooling airflow between the crankcase and the cover. The centrifugal fan includes a hub defining a rotational axis, a plurality of blades arranged about the rotational axis, and a screen coupled to the hub and blades for co-rotation therewith. The hub, the blades, and the screen are integrally formed as a single piece.

Other features and aspects of the invention will become apparent by consideration of the following detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an engine including a centrifugal fan of the present invention.

FIG. 2 is an exploded perspective view of the engine of FIG. 1, illustrating the centrifugal fan.

FIG. 3 is a top perspective view of the centrifugal fan of FIG. 2.

FIG. 4 is a bottom perspective view of the centrifugal fan of FIG. 2.

FIG. 5 is a front plan view of the centrifugal fan of FIG. 2.

FIG. 6 is a bottom plan view of the centrifugal fan of FIG. 2.

FIG. 7 is a top view of a splitter blade superimposed on a main blade, illustrating the camber of the splitter blade and the main blade.

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

FIG. 1 illustrates an engine 10 including a crankcase 14 and a crankcase cover 18 that at least partially encloses the crankcase 14. The engine 10 is a single-cylinder engine; however, the engine 10 may alternatively include two cylinders arranged in a V-twin configuration, or more than two cylinders in any of a number of different configurations (e.g., inline, horizontally opposed, etc.), and so forth. With reference to FIG. 2, the engine 10 also includes a crankshaft 22 that is rotatable about an axis 26 while the engine 10 is in use. The engine further includes a centrifugal fan 30 that is coupled for co-rotation with the crankshaft 22. Particularly, the centrifugal fan 30 includes a hub 34 having an aperture 38 through which the crankshaft 22 is inserted. The hub 34 may be coupled to the crankshaft 22 by any suitable means (e.g., fasteners, flanges, keyways, cooperating splines, etc.). Although not shown, a flywheel may optionally be included between the centrifugal fan 30 and the crankshaft 22.

With reference to FIG. 3, the centrifugal fan 30 includes an inlet portion 42 through which axially-directed air is drawn and an outlet portion 46 through which the cooling airflow is discharged in a radially outward direction. The cooling airflow passes through an airspace defined between the crankcase 14 and the crankcase cover 18 in order to remove waste heat from the crankcase 14. Now referring to FIG. 6, the centrifugal fan 30 further includes a plurality of main blades 50 arranged about the axis 26 and a plurality of splitter blades 54 arranged about the axis 26. The main blades 50 and the splitter blades 54 are alternately spaced such that a single splitter blade 54 is positioned between adjacent main blades 50. Alternate constructions of the centrifugal fan 30 may include more than one splitter blade 54 between adjacent main blades 50, or may not include any splitter blades 54 at all. Each of the main blades 50 includes a suction surface 58, a pressure surface 62 opposite the suction surface 58, a leading edge 66, and a trailing edge 70, with the collection of trailing edges 70 of the main blades 50 coinciding with the outlet portion 46 of the centrifugal fan 30. Similarly, each of the splitter blades 54 includes a suction surface 74, a pressure surface 78 opposite the suction surface 74, a leading edge 82, and a trailing edge 86, with the collection of trailing edges 86 of the splitter blades 54 coinciding with the outlet portion 46 of the centrifugal fan 30. The leading edge 66 of each of the main blades 50 is integral with the hub 34, and the leading edge 82 of each of the splitter blades 54 is spaced from the hub 34. Accordingly, the main blades 50 are longer than the splitter blades 54.

With continued reference to FIG. 6, each of the main blades 50 is curved in the direction of rotation of the centrifugal fan 30, indicated by arrow “A.” The extent of this curvature is known in the art as “camber,” which is measured with reference to a nose-tail line 90 and a mean line 94. The nose-tail line 90 is a straight line that extends from the trailing edge 70 to the leading edge 66, while the mean line 94 extends from the trailing edge 70 to the leading edge 66, half-way between the suction surface 58 and the pressure surface 62. Camber is a non-dimensional quantity defined as a perpendicular distance “D1” between the mean line 94 and the nose-tail line 90 divided by the length of the nose-tail line 90, otherwise known as the blade “chord.” Generally, the larger the non-dimensional quantity of camber, the greater the curvature of the blade. In the illustrated construction, the camber of the main blades 50 is between about 0.1 and about 0.2. Preferably, the camber of the main blades 50 is about 0.16.

With continued reference to FIG. 6, the splitter blades 54 are also curved in the direction of rotation of the centrifugal fan 30, as indicated by arrow A. However, the camber of the splitter blades 54 is not measured independently of the main blades 50, using the procedure described above. Rather, the geometry of the splitter blades 54 is defined by the geometry of the main blades 50 because the splitter blades 54 are essentially “shortened” main blades 50. Like the main blades 50, each of the splitter blades 54 defines a mean line 98 extending from the leading edge 82 to the trailing edge 86, half-way between the suction surface 74 and the pressure surface 78 of the splitter blade 54. However, a nose-tail line 100 drawn from the leading edge 82 of the splitter blade 54 to the trailing edge 86 of the splitter blade 54 is not used to calculate the curvature of the splitter blade 54 (FIG. 7). Rather, the curvature of the splitter blades 54 is described in terms of the main blade nose-tail line 90, drawn as if the trailing edge 86 of the splitter blade 54 was the trailing edge 70 of the main blade 50.

With reference to FIGS. 6 and 7, to describe the camber of the splitter blade 54 relative to the camber of the main blade 50, the shape of the splitter blade 54 is superimposed on the shape of the main blade 50. To do this, the splitter blade 54 mean line 98 is rotated about the axis 26 from its location shown in FIG. 6 to a location where at least a portion of the splitter blade mean line 98 near the leading edge 82 of the splitter blade 54 is superimposed on the main blade mean line 94 (FIG. 7). The splitter blade mean line 98 has a substantially parallel curvature to that of the main blade mean line 94, at least in the portion of the splitter blade mean line 98 near the leading edge 82, because the splitter blade 54 shares some of its geometry with the main blade 50.

With continued reference to FIG. 7, the camber of the splitter blade 54 is the same as the camber of the main blade 50. To calculate the camber of the splitter blade 54, another nose-tail line 102 is drawn between the leading edge 66 of the main blade 50 and the trailing edge 86 of the splitter blade 54. This nose-tail line 102 is representative of the chord of the splitter blade 54, if the splitter blade 54 was not shortened and its leading edge geometry was identical to that of the main blade 54. Further, a perpendicular distance “D2” is measured from this nose-tail line 102 to the splitter blade mean line 98. The camber of the splitter blade 54 is then the ratio of the perpendicular distance D2 to the length of the new nose-tail line 102. Because the camber of the splitter blade 54 is the same as the camber of the main blade 50 in the illustrated construction, the nose-tail line 102 is collinear with the nose-tail line 90 of the main blade 50. The perpendicular distance D2 is therefore equal to the perpendicular distance D1. In the illustrated construction, the camber of the splitter blade 54 is between about 0.1 and about 0.2. Preferably, the camber of the splitter blades 54 is about 0.16, the same as the camber of the main blades 50.

With reference to FIGS. 3 and 4, each of the main blades 50 and the splitter blades 54 includes a top edge 106 and a bottom edge 110 spaced axially from the top edge 106. The top edge 106 of each of the main and splitter blades 50, 54 includes a plurality of notches 114 configured to allow fluid communication between adjacent blades 50, 54. This fluid communication equalizes static pressure between adjacent blades 50, 54 to provide a more uniform flow rate of the cooling airflow discharged from the centrifugal fan 30.

With continued reference to FIG. 3, the centrifugal fan 30 includes a plurality of concentric rings 118 comprising a screen 122. The screen 122 prevents an operator from accidentally contacting the blades 50, 54 and prevents large debris from being drawn into the inlet portion 42 and damaging the centrifugal fan 30. The concentric rings 118 are attached to the top edge 106 of each of the main and splitter blades 50, 54 between adjacent notches 114. The main blades 50 act as structural members to rigidly interconnect the hub 34 and the screen 122 such that the hub 34, the main blades 50, and the screen 122 all co-rotate with the crankshaft 22 about the axis 26. Unlike the main blades 50, the splitter blades 54 are not directly attached to the hub 34 and are therefore supported only by their attachment with the screen 122.

The centrifugal fan 30 of the present invention, including the combination of features described above, is formed as a single piece by a suitable molding process such as injection molding. The centrifugal fan 30 may be molded with a relatively simple mold (not shown) that is separable into first and second mold halves. The mold halves may be brought together or separated from one another along a mold axis that is coaxial with the rotational axis 26 of the centrifugal fan 30. With reference to FIG. 5, the main blades 50 and splitter blades 54 have a thickness “t” that varies from the top edge 106 to the bottom edge 110. More specifically, the thickness “t” is greater at the top edge 106 than at the bottom edge 110. This thickness variation defines a draft in the direction of mold separation that facilitates ejection of the centrifugal fan 30 from the mold.

In contrast to conventional fans (not shown), which require multiple manufacturing steps before the final product is complete, the single piece design is greatly simplified. The molding process allows for accurate and consistent formation of the various features described above without the need for separate machining and fastening operations. In addition, conventional fans often include a base portion (e.g., a flat disk) to which all other components are connected. In the single piece design according to the present invention, the hub 34, the blades 50, 54, and the screen 122 are all integrally formed and do not require any additional base portion. As such, the manufacturing of the centrifugal fan 30 of the present invention is greatly simplified, and material cost and tolerance requirements are reduced.

Various features of the invention are set forth in the following claims. 

We claim:
 1. A centrifugal fan for use with an engine, comprising: a hub including a rotational axis; a plurality of blades arranged about the rotational axis and coupled to the hub for co-rotation therewith, wherein each blade includes a pressure surface, a suction surface opposite the pressure surface, a leading edge defining a boundary between the suction surface and the pressure surface, and a trailing edge opposite the leading edge; and a screen coupled to the hub and the blades for co-rotation therewith, wherein the hub, the blades, and the screen are integrally formed as a single piece, wherein the plurality of blades comprises a plurality of main blades and a plurality of splitter blades, wherein the leading edge of each main blade is integral with the hub and wherein the leading edge of each splitter blade is spaced from the hub.
 2. (canceled)
 3. The centrifugal fan of claim 1, wherein each of the blades defines a nose-tail line connecting the leading edge and the trailing edge, the nose-tail line being a straight line and defining a length; and a mean line half-way between the pressure surface and the suction surface and intersecting the nose-tail line at the leading edge and the trailing edge.
 4. (canceled)
 5. The centrifugal fan of claim 3, wherein each of the blades includes a camber between about 0.1 and about 0.2.
 6. The centrifugal fan of claim 5, wherein the plurality of blades comprises a plurality of main blades and a plurality of splitter blades, wherein the camber of the splitter blades is the same as the camber of the main blades.
 7. The centrifugal fan of claim 4, wherein the main blades and the splitter blades are alternately spaced about the rotational axis.
 8. The centrifugal fan of claim 1, wherein the screen includes a plurality of concentric rings coaxial with the rotational axis and interconnected by the blades.
 9. The centrifugal fan of claim 1, wherein each of the blades includes at least one notch in a top edge of the blade, the notch configured to allow an airflow to pass between adjacent blades.
 10. An engine comprising: a crankcase; a cover at least partially enclosing the crankcase; and a centrifugal fan that is rotatable while the engine is in use for discharging a cooling airflow between the crankcase and the cover, the centrifugal fan including a hub including a rotational axis, a plurality of blades arranged about the rotational axis and coupled to the hub for co-rotation therewith, wherein each blade includes a pressure surface, a suction surface opposite the pressure surface, a leading edge defining a boundary between the suction surface and the pressure surface, and a trailing edge opposite the leading edge, and a screen coupled to the hub and the blades for co-rotation therewith; wherein the hub, the blades, and the screen are integrally formed as a single piece, and wherein the plurality of blades comprises a plurality of main blades and a plurality of splitter blades, and wherein the leading edge of each main blade is integral with the hub and wherein the leading edge of each splitter blade is spaced from the hub.
 11. (canceled)
 12. The engine of claim 10, wherein each of the blades defines a nose-tail line connecting the leading edge and the trailing edge, the nose-tail line being a straight line and defining a length; and a mean line half-way between the pressure surface and the suction surface and intersecting the nose-tail line at the leading edge and the trailing edge.
 13. (canceled)
 14. The engine of claim 12, wherein each blade includes a camber between about 0.1 and about 0.2.
 15. The engine of claim 14, wherein the plurality of blades comprises a plurality of main blades and a plurality of splitter blades, wherein the camber of the splitter blades is the same as the camber of the main blades.
 16. The engine of claim 10, wherein the main blades and the splitter blades are alternately spaced about the rotational axis.
 17. The engine of claim 10, wherein the screen includes a plurality of concentric rings coaxial with the rotational axis and interconnected by the blades.
 18. The engine of claim 10, wherein each of the blades includes at least one notch in a top edge of the blade, the notch configured to allow an airflow to pass between adjacent blades.
 19. The engine of claim 10, wherein each of the blades includes a top edge attached to the screen and a bottom edge, and wherein the bottom edge of each of the blades is a free edge.
 20. The engine of claim 19, wherein the bottom edge includes a thickness less than that of the top edge. 